I'm wondering if this is a "Down Under" thing, or whether you know it by a different name.

Here's what I remember:

For the mother plant you add ground ginger, sugar and water, and I remember sultanas. The recipes I find now add yeast and no sultanas, but I know my dad didn't use yeast.

Every day for a week you feed the plant with ginger and sugar. At the end of the week you strain the mother plant, then add sugar, water and lemon juice to half of the plant to make up your ginger ale.

After making up your ginger beer/ale, you use the other half to start all over again.

Does that help?